The Mesozoic northwestward amalgamation and Cenozoic southeastward rifting and collison of the South China Sea terrain system and its influence on the formation and evolution of the South China Sea basin are discussed based on a geophysical data set, dredged rocks and sediment cores obtained during Chinese and joint investigation in the South China Sea, as well as the results of exploration along the margins. Two geological interpretation profiles from north to south of the South China Sea are chosen to illustrate the origin and geodynamic process of the South China Sea.

In the terrain system, Dongsha terrain, Zhongska-Xisha (Macclesfield Bank-Paracel Is.) terrain, Nansha (Spratley Is.) terrain and North Palawan terrain have a close relation to each other and no relation to South Palawan and Borneo in the late Mesozoic. During Early Cretaceous, these terrains underwent the same tectonic event and constituted an united terrain, although each has its own characteristics.

After the northwestward amalgamation and collison along the South China continental margin in the Late Cretaceous, the united terrain began separating and rifting to the south in the Cenozoic, thus leading to the formation of the South China Sea basin.

The eastern area of the South China Sea basin has the characteristics of seafloor spreading, while the western one has the characteristics of crustal rifting. The rifting separated the Zhongsha-Xisha (Macclesfield Bank-Paracel Is.) terrain, Nansha (Spratley Is.) terrain and North Palawan terrain from north continental margin, and forced them move to the south. Finally in late middle Miocene, the Nansha (Spratley Is.) terrain and North Palawan terrain collided with the Cagayan arc and Sabah-Sarawak terrain along Palawan Trough and solidified. By then, the large scale horizontal movement of terrains stopped.